Evaluating x-ray detectors for radiographic applications: A comparison of ZnSCdS:Ag with and screens

Abstract

ZnSCdS:Ag was evaluated as a radiographic image receptor and was compared with Gd2O2S:Tb and Y2O2S:Tb phosphors often used in radiography. The evaluation of a radiographic receptor was modelled as a three-step process: (i) determination of light output intensity as related to the input radiation dose, (ii) determination of visible light characteristics with respect to radiographic optical detectors, and (iii) determination of image information transfer efficiency. The light intensity emitted per unit of x-ray exposure rate was measured and theoretically calculated for laboratory prepared screens with coating thicknesses from 20 to 220 mg cm-2 and tube voltages from 50 to 250 kVp. ZnSCdS:Ag light intensity was higher than that of Gd2O2S:Tb or Y2O2S:Tb for tube voltages less than 70 and 80 kVp respectively. ZnSCdS:Ag displayed the highest x-ray to light conversion efficiency (0.207) and had optical properties close to those of Gd2O2S:Tb and Y2O2S:Tb, and its emission spectrum was well matched to optical detectors. The image information transfer properties described by the modulation transfer function, the quantum noise transfer function, and the detective quantum efficiency were calculated for both general radiographic and mammographic conditions and were found to be intermediate between those of Gd2O2S:Tb and Y2O2S:Tb screens. Conclusively, ZnSCdS:Ag is an efficient phosphor well suited to radiography.

Integrated model for estimating phosphor signal and noise transfer characteristics on medical images: application to CdPO3Cl:Mn phosphor screens

“…However NTF decreases more slowly than the corresponding MTF At 100 lp mm 1, the NTF of the 21 mg cm 2 screen is equal to 0.4, whereas the corresponding MTF is 0.26. This difference, which is compatible with data published in previous studies (KANDARAKIS et al, 1997), indicates that noise passes more efficiently than signals through a phosphor screen.…”

“…The output noise can be expressed by the noise amplitude spectrum Ap(u, w), the noise power (or Wiener) spectrum Wp(u, w) (square of Ap) or the noise transfer function Np (KANDARAKIS et al, 1997;KALWAS et al, 1999), defined as we(~, w)…”

“…The noise power spectrum Wp(u, w) (and NTF) can be expressed in terms of (I)2, Mp(u, w) and of intrinsic parameters related to the X-ray absorption and X-ray-to-light conversion processes (SHAW and VAN METTER, 1984;KANDARAKIS et al, 1997;KALIVAS et al, 1999). Thus the output signal-to-noise ratio and the detective quantum efficiency can be expressed as follows:…”

“…The latter gives MTF as a function of SWRF. MTF data obtained in this way were corrected by being divided by the MTF of the scanner and the MTF of the film, both measured in the same way CAVOURAS et al, 1997).…”

X-ray imaging resolution of phosphor screens prepared with different grains size and shape of granular Lu2O3:Eu

“…The sedimentation was achieved by using a mixture consisting of 1000 ml of deionized water, 20 ml of Na 2 SiO 3 , and the appropriate amount of phosphor powder in a glass tube of 110 cm height. The substrate was placed at the bottom of the tube [23,24] and secured using a silicone optical compound (Visilox V-788) as an adhesive media between substrate and holder. This compound can be easily removed afterwards by using an alcohol based solution without leaving any light absorbing stains.…”